The code I am using is below and the window remains docked to the right side of the window no matter how I change the value… NppTbMsg.DWS_DF_CONT_LEFT or NppTbMsg.DWS_DF_CONT_TOP
for example and the window still stays docked to the right-hand side. Is there a better way of doing this? I simply want a window that cannot be moved which will showup in the middle of the notepad++ screen,

no, the reason might be that npp remembers it last location.
Open the config.xml with an editor other than npp and delete the entry
of your plugin under GUIConfig name=“DockingManager” section.
Start npp and open your plugin window and it should dock on the left side.